1. Field of the Invention
This invention relates to a solenoid actuator for reciprocatingly driving a driven member by an electromagnetic force.
2. Description of the Prior Art
Conventionally, a solenoid actuator of this kind has been proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 10-294214, which is applied to a valve-actuating mechanism for driving a valve of an internal combustion engine to open and close the valve. This valve-actuating mechanism includes an armature in the form of a rectangular plate, and upper and lower electromagnets, rectangular in cross-section, for vertically attracting the armature, and upper and lower rods extending upward and downward from the armature, respectively. The upper and lower rods are circular in cross-section, and the lower rod is linked to the valve.
When the solenoid actuator described above is in operation, the upper and lower electromagnets are alternately energized and deenergized to alternately attract the armature whereby the armature performs vertical reciprocation motion. In accordance with the vertical reciprocating motion of the armature, the upper and lower rods slide upward and downward to open and close the valve.
In the solenoid actuator having the armature and electromagnets, rectangular in cross-section, when the armature performs vertical reciprocating motion during operation of the solenoid actuator, it is necessary to prevent the armature from rotating about an axis extending along the direction of the vertical reciprocating motion thereof. This is because if such a rotation occurs, the armature rectangular in cross-section abuts components therearound, such as a casing housing the armature, to cause interference therewith. This can prevent smooth driving of the driven member, such as the valve, or cause breakage of the armature and/or the casing.
It is an object of the invention to provide a solenoid actuator which is capable of smoothly driving a driven member, with enhanced durability, and at the same time permits the stroke of the driven member to be changed with ease.
To attain the above object, the present invention provides a solenoid actuator for driving a driven member by an electromagnetic force such that the driven member performs reciprocating motion, comprising:
at least one electromagnet;
an armature connected to the driven member, for performing reciprocating motion in accordance with energization and deenergization of the at least one electromagnet to thereby drive the driven member such that the driven member performs the reciprocating motion, the armature having two end faces extending in parallel with each other in a direction orthogonal to a direction of the reciprocating motion thereof; and
guide means having two guide surfaces opposed to the two end faces of the armature, respectively, the two guide surfaces being formed with a total of at least three protrusions at respective locations each of the two guide surfaces being formed with at least one of the at least three protrusions, the guide means slidably guiding the reciprocating motion of the armature in a state of the two end faces of the armature being in partial contact with the at least three protrusions of the two guide surfaces of the guide means.
According to this solenoid actuator, in accordance with energization and deenergization of the at least one electromagnet, the armature is reciprocatingly moved while being guided by the guide means to drive the driven member such that the driven member performs reciprocating motion. During the reciprocating motion of the armature, the armature is guided by the guide means in a state of the two parallel end faces thereof being in partial contact with the at least three protrusions of the two guide surfaces of the guide means. Therefore, even if a rotational force for rotating the armature about an axis along the direction of the reciprocating motion thereof is applied to the armature, the guide means inhibits the armature from rotating about the axis. Further, since the armature slides in a state in partial contact with each of the at least three protrusions on the guide surface, the armature receives a small sliding resistance from the guide means. These features ensure the smooth opening and closing operations of the driven member, and at the same time enhance the durability of the solenoid actuator.
Preferably, the at least one electromagnet comprises two electromagnets arranged on opposite sides of the armature in the direction of the reciprocating motion thereof, and fixed to each other with the guide means sandwiched therebetween.
According to this preferred embodiment, two electromagnets are fixed to each other with the guide means sandwiched therebetween, and the guide means serves as a spacer defining a distance between the two electromagnets. This makes it possible to change the distance over which the armature reciprocates, i.e. the stroke of the driven member, simply by changing the guide means to another type having a different width in the direction of the reciprocating motion thereof. Therefore, it is possible to change the valve lift amount of the driven member more easily than in the case where the core of each electromagnetic valves is changed.
Preferably, the guide means comprises two guides arranged such that the two guides are opposed to the two end faces of the armature, respectively, and the two guide surfaces are respective surfaces of the two guides facing toward the two end faces of the armature.
More preferably, each of the respective surfaces of the two guides is formed with at least one groove extending along the direction of the reciprocating motion of the armature, a protruding member being fixed to each of the at least one groove, the protruding member having a fitting portion and a guide portion semicircular in cross section and integrally formed with the fitting portion, and each of the at least three protrusions is the guide portion semicircular in cross section and in line contact with a corresponding one of the two end faces of the armature.
Preferably, the solenoid actuator includes a shaft connecting the armature to the driven member and having a flange formed at one end thereof, and the armature is formed with a through hole extending through a central portion thereof along the direction of the reciprocating motor thereof and has a portion surrounding the through hole, the end of the shaft being fitted in the through hole such that the flange abuts the portion surrounding the through hole to thereby support the armature.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.